Hydrogen halide recovery



Aug. 15,1944.'

K. H. HAcHMuTH HYDROGEN HALIDE RECOVERY Filed March 10, 1942 aadd'lms Patented Aug. 15, 1944 HYDROGEN nALmE RECOVERY Karl Hachmuth, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application March 10, 1942, Serial No. 434,125

4 Claims.

This invention relates to the recovery of anhydrous hydrogen halide from admixture with light hydrocarbons and especially to the recovery of anhydrous hydrogen chloride from a hydrocarbon conversion process, such as processes for the alkylation or isomerization of hydrocarbons such as parains and olens wherein anhydrous hydrogen chloride is commingled with reactants in the conversion zone.

In many arts and especially in the eld of hydrocarbon conversion such as dehydrohalogenation, alkylation, isomerization, etc., anhydrous hydrogen halide, generally hydrogen chloride, is present in the reaction etlluent in admixture with light hydrocarbons of such boiling point that they can beseparated from the hydrogen halide only with great difficulty, and at great expense.

In most cases separation by fractional distillation is out of the question because of the ex' cessive expense involved and because of the amounts of refrigeration required for liquefaction and the closeness of the boiling points of the components of the mixture. Also frequently azeotropes of the hydrogen halide -and the light hydrocarbons are formed whichmake impossible the separation of the components by ordinary means.

For example, in isomerization and alkylation processes using anhydrous hydrogen chloride as a promoter for the metal halide catalyst such as aluminum chloride, the light hydrocarbons formed and the anhydrous hydrogen chloride are separated from the remainder of the materials. In recycling the hydrogen chloride, a portion of the stream must bevented to prevent too great an accumulation of the lighter hydrocarbons, In the past the hydrogen c hloride in the vent stream was either wasted lor recovered as aqueous hydrochloric acid which cannot be reused in the process. Also it has been common to remove anhydrous hydrogen halide from admixture with hydrocarbons by giving the mixture an alkali wash. This wastes both alkali and4 the hydrogen halide. My invention comprises a process for the recovery of the hydrogen chloride in an anhydrous state which permits its reuse in the process.

In numerous other processes, there are obtained fractions including anhydrous hydrogen halide and hydrocarbons which are either normally gaseous or for other reason diicult or impossible'to separate from the hydrogen halide by known methods.

Thus, in the dehydrohalogenation of halogenated hydrocarbons to produce unsaturated hydrocarbons such as is used in the manufacture of aliphatic conjugated dioleflns, the reaction effluent may consist of a mixture of anhydrous hydrogen halide and the unsaturated hydrocarbon, such as for example a mixture of HCl and butadiene-L3.

My invention maybe applied to the processes mentioned above and to other processes wherein it is desired to resolve a. mixture of anhydrous hydrogen halide and a hydrocarbon which may be normally gaseous or have a boiling point close vto that of the hydrogen halide or for other reason be diflicult to separate therefrom by conventional methods.

The principal object of my invention therefore is to provide an improved process for the separation of anhydrous hydrogen halide from admixture with hydrocarbon.

Another object is to provide an improved method of separation of anhydrous hydrogen halide which is normally gaseous, from admixture with normally gaseous hydrocarbon, especially normally gaseous hydrocarbons of petroleum and natural gas origin such as the lighter paraflins namely methane, ethane, propane, n-butane and isobutane, and the lighter mono-olens namely ethylene, propylene, butene-l, butene-2, and isobutene.

Still another object is to provide a process of the foregoing type for the recovery of anhydrous hydrogen chloride.

Still another object is to provide a process of the foregoing type for the recovery of anhydrous hydrogen fluoride.

Still another object is to provide a process of the foregoing type for the recovery of anhydrous hydrogen halide from hydrocarbon conversion reaction mixtures.

Numerous other objects will more fully hereinafter appear. y

In the accompanying drawing there is portrayed diagrammatically one form of equipment for carrying out the present invention.

I have now found that anhydrous hydrogen halide may be recovered in substantially pure state from admixture with hydrocarbon by selecpressures of atmospheric up to 100 vpounds per square inch gage. However in certain instances it may be'desirable to operate at pressures as high as '800 pounds per square inch gage, particularly when the products to be treated are at a high pressure and the resultant hydrogen halide-free products are to be used in subsequent high pressure processes. Temperatures as high as about 150 F. may be used. However it is preferable to operate attemperatures below 150" F. but above the freezing point (about 60 F.) of the acid.

My process is applicable primarily to the separation of anhydrous hydrogen chloride but may be applied to the other normally gaseous and therefore difli'cultly condensible hydrogen halides, namely, anhydrous hydrogen bromide and anhydrous hydrogen iodide.

My process is also applicable to the separation of anhydrous hydrogen fluoride which is a liquid at ordinary temperature'and pressure.

The boiling points of the several .hydrogen halides are as follows:

HCl -85 HBr -67 HI -35.5 I-IF -|-19.4

The boiling point of the glacial acetic acid is 118.1" C. (244.5" F.). 'y

The boiling points of the several normally gaseous paraflin, mono-,olefin and diolen hydrocarbons apt to be encountered, either singly or in admixture, when dealing with separation of the normally gaseous anhydrous hydrogen haiides are as follows:

C. Methane -161.4 Ethane A88.3 'Propane 4- 44.1 N-butane 0 6 Isobutane; 10.2 Ethylene f 103.9 Propylene 48.0 Butene-l 6.7 Butene-2 1.0 Isobutene 6.6 Butarliene 1 0 The hydrocarbons apt tobe encountered in admixture with hydrogen iiuoride may be as follows:

` C. Isopentane 28.0 Y Neopentane Y 9 5 Pentene-l -l 30.0 Isopropylethylene .20.1

Usually in the case of normally gaseous hydrocarbons and hydrogen halide the mixture will enter the absorbing unit in the gaseous form.

Referring now to the drawing, a feed of hydro-v carbons to be converted may enter a reactionA chamber 2 vla line I, anhydrous hydrogen chloride entering via line 3 if desired. The reaction pass via line 8 into the absorbing unit 9. A slmif lar mixture from an outside source may be introduced, if desired, via line Ill.

In the absorber 9 the gaseous mixture passes upwardly countercurrently to downwardly flowling glacial acetic acid introduced viafline II. The hydrocarbon gases, essentially free from the hydrogen chloride, leave via line I 2, l i

Thev HCl-enriched glacial acetic acidexits viav line` I3 and passes into stripping unit yI4 wherev it is stripped in anysuitable manner of itsanhyi drous hydrogen chloride which leaves via line I5. The stripped glacial acetic acidmay leave via line I6 and be recycled via line Il to the absorption unit 9.

Example A gaseous vent mixture consisting of 50 per. cent anhydrous hydrogen chloride and 50 per cent of light parailin hydrocarbons essentially methane and ethane was passed lthrough an absorption .tower where it was contacted with glacial acetic acid(99%) at 120 F. using a pressure 'of 50 lbs. per sq. in gage and a glacial acetic acid circulationof v55. gallons per 1000 cubic feet of the mixture fed.` ',Ihe absorption tower con-r tained 40 trays. .A v97% recovery of 98% pure anhydrous hydrogeny chloride was obtained.

The advantages` of my` invention are numerous. Among them are `the unusually vclean-cut separation'efected andthe high yield of the anhydrous hydrogen halide in essentially pureform. Another advantage is the simplicity of the operation and the small investment in equipment required. Numerous other advantages will be ap-k parent to those skilled in .the art from the foregoing disclosure. i l

It will be understood that the absorptionand stripping operations are conducted in a conventional manner except that a particular stream is being treated witha particular selective solvent. The stripping step will of course generallybe conducted by heating the enriched acetic acid to a suitable temperature preferably substantially below the boiling pointl of pure acetic acid but sum'- ciently elevated to drive 01T substantially all'the dissolved hydrogen halide ,contentthereo VBy glacial acetic acid" as used herein, I meanl a product containing at least about per cent by weight of the pure chemical acetic acid, the diluent being mainly water. `I vprefer to use acetic acid of 99 per cent by weight or greater purity in my invention. .v

Iclaim:

1. A process for the separation-of a liquid mix-l. ture of an anhydrous hydrogen halide .andfffa' hydrocarbon having a boiling`=pointr close thereto,V4 which comprises treating the saidlllquid mixture with liquid glacial acetic acidto fi t aiselective il riffs.'

removal of liquid anhydrous hydrogen halide from said liquid hydrocarbon.-

2. A process for the separation. of a liquid mixture of anhydrous hydrogen halide and a light hydrocarbon which comprises treating said liquid mixture under absorbing conditions with liquid glacial acetic acid and under a pressure suicient to maintain liquid phase and not greater than about 800 pounds gage and at temperatures above the freezing point of the acid to about 150 F. to' selectively dissolve said hydrogen halide from said yliquid light hydrocarbon.

3. A process for removing hydrogen chloride from a low boiling liquid hydrocarbon mixture, which comprises contacting a liquid hydrocarbon material containing anhydrous hydrogen chloride with liquid glacial acetic acid undericonditions liquid hydrocarbon material substantially free from hydrogen iluoride.

KARL H. HACHMUTH. 

